Class9- GPRS Explained
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Transcript of Class9- GPRS Explained
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 1/17
General Packet Radio Service
(GPRS)
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 2/17
MAC: TBF Establishment
• MS initiated
– One Phase Access, or
– Two Phase Access
MS BSS MS BSS
PACKET CHANNEL REQUESTPRACH
PACKET UPLINK ASSIGNMENT PAGCH
TBF Est. By MS: One Phase Access
PACKET CHANNEL REQUESTPRACH
PACKET RESOURCE REQUESTPACCH
PACKET UPLINK ASSIGNMENT PACCH
TBF Est. By MS: Two Phase Access
PACKET UPLINK ASSIGNMENT PAGCH
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 3/17
MAC: TBF Establishment
• Network initiated
MS BSSPACKET PAGING REQUEST PPCH
PACKET CHANNEL REQUESTPRACH
PACKET PAGING RESPONSEPACCH
PACKET DOWNLINK ASSIGNMENT PACCH or PAGCH
TBF Est. By Network
PACKET IMMEDIATE ASSIGNMENT PAGCH
7/29/2019 Class9- GPRS Explained
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MAC: Channel Access & Resource
Allocation
• Slotted Aloha
– Used in PRACH• MSs send packets in uplink direction at the beginning of a slot
•
Collision: Back off -> timer (arbitrary) -> re-transmit• Time Division Multiple Access (TDMA)
– Predefined slots allocated by BSS
– Contention-free channel access
– All logical channels except PRACH
7/29/2019 Class9- GPRS Explained
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QoS Support
• End-to-end QoS may be specified by Service Level Agreements
• Assumes that IP multimedia applications are able to – Define their requirements
– Negotiate their capabilities – Identify and select available media components
• GPRS specifies signaling that enable support for varioustraffic streams – Constant/variable bit rate
– Connection oriented/connection less – Etc.
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 6/17
QoS Profile for GPRS Bearers
• Describes applications characteristics and QoSrequirements
• 4 parameters: – Service precedence
• 3 classes
– Reliability parameter • 3 classes
– Delay parameters• 4 classes
– Throughput parameter • Maximum and mean bit rates
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 7/17
QoS Profile for GPRS Bearers
• QoS profile is included in Packet Data Protocol
(PDP) context
• Negotiation managed through PDP procedures
(activation, modification and deactivation)
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 8/17
Packet Classification and
Scheduling
• TBF tagged with TFI
• TFI different for each TBF
• Packet scheduling algorithms are not defined by the
standard; defined and implemented by GPRS networkdesigners and carriers
• GPRS *can* enable per-flow quantitative QoS services
with proper packet classification and scheduling
algorithms...Hmmm.
7/29/2019 Class9- GPRS Explained
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Mobility Management
• Two procedures:
– GPRS Attach/Detach (towards SGSN/HLR)
• Makes MS available for SMS over GPRS
• Paging via SGSN• Notification of incoming packet
– PDP Context Activation/Deactivation
• Associate with a GGSN
• Obtain PDP address (e.g. IP)
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 10/17
GPRS Mobile “Station” States
• GPRS protocol stack (MS) can take on 3 differentstates
– IDLE
–STANDBY
– ACTIVE/READY
• Data can only be transmitted in the ACTIVE state
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 11/17
Routing to MS
• IDLE state
– No logical PDP context activated
– No network address (IP) registered for the terminal
– No routing of external data possible – Only multicast messages to all GPRS handsets available
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 12/17
Routing to MS
• STANDBY state
– Only routing area is known
• RA is defined by operator => allows individual optimizations
–When downlink data is available, packet pagingmessage is sent to routing area
– Upon reception, MS sends it's cell location to the SGSN
and enters the ACTIVE state
7/29/2019 Class9- GPRS Explained
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Routing to MS
• ACTIVE state
– SGSN knows the cell of the MS
– PDP contexts can be activated/deactivated
–
Can remain in this state even if not data is transmitted(controlled by timer)
7/29/2019 Class9- GPRS Explained
http://slidepdf.com/reader/full/class9-gprs-explained 14/17
PDP Contexts
• Packet Data Protocol (PDP)
– Session
– Logical tunnel between MS and GGSN
– Anchored GGSN for session
• PDP activities
– Activation
–
Modification – Deactivation
7/29/2019 Class9- GPRS Explained
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PDP Context Procedures
• MS initiated
MS BSS SGSN GGSN Activate PDP Context Request
Create PDP Context
Request
Create PDP Context
Response
Activate PDP Context Accept
7/29/2019 Class9- GPRS Explained
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PDP Context Procedures
• GGSN initiated
MS BSS SGSN GGSN
Activate PDP Context RequestCreate PDP Context
Request
Create PDP Context
Response Activate PDP Context Accept
Packets from ext. nw.
PDU notification req.
PDU notification resp.
Request PDP Context activation
7/29/2019 Class9- GPRS Explained
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Secondary PDP Contexts
• Used when the QoS requirements differ from
Primary PDP Context
– Same IP address
– Same APN
• E.g., for IMS; signaling on primary PDP context
and user data on secondary PDP context